Rare Green Comet C/2025 R2 (SWAN) Approaches Earth, Offering Unique Viewing Opportunity

Comet C/2025 R2 (SWAN), a long-period comet with an orbital period of approximately 22,554 years, was discovered on September 11, 2025, by amateur astronomer Vladimir Bezugly using images from the Solar Wind Anisotropies (SWAN) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft. The comet exhibits a greenish coma and a tail extending over 2 degrees in length.

As of late September, Comet SWAN is located near the star Spica in the Virgo constellation. While currently not visible to the naked eye, it is expected to brighten as it approaches Earth. The comet will make its closest approach to Earth on October 21, 2025, at a distance of approximately 0.27 astronomical units (AU). During this period, it may reach a magnitude of 4, potentially making it visible without optical aid under dark skies.

Observers in the Northern Hemisphere may have the best chance to view the comet around October 2, 2025. Using binoculars after sunset, skywatchers should look toward the southwest part of the sky. On October 2, the comet will pass near Zubenelgenubi, the alpha star of the Libra constellation. Additionally, around October 20-23, 2025, Comet SWAN will be visible alongside Comet C/2025 A6 (Lemmon), coinciding with the peak of the Orionid meteor shower. This convergence offers a rare opportunity to observe two bright comets and a meteor shower simultaneously.

Comet SWAN's green coloration is due to the presence of diatomic carbon (C2) in its coma, which emits a green glow when excited by sunlight. This characteristic is common among comets as they approach the Sun. Given its long orbital period, this will be a once-in-a-lifetime event for observers.